<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=<div>, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        div:before{
            width:100px;
            height:100px;
            background:red;
            content:"前面";
            display：block;
        }
        div:after{
            content:"后面";
            display：block；
            width:100px;
            height:50px;
            background:yellow;
        }
           
       
    </style>
</head>
<body>
    <div>
    content
    </div>
</body>
</html>
